bus: mhi: host: Fix race between unprepare and queue_buf

A client driver may use mhi_unprepare_from_transfer() to quiesce
incoming data during the client driver's tear down. The client driver
might also be processing data at the same time, resulting in a call to
mhi_queue_buf() which will invoke mhi_gen_tre(). If mhi_gen_tre() runs
after mhi_unprepare_from_transfer() has torn down the channel, a panic
will occur due to an invalid dereference leading to a page fault.

This occurs because mhi_gen_tre() does not verify the channel state
after locking it. Fix this by having mhi_gen_tre() confirm the channel
state is valid, or return error to avoid accessing deinitialized data.

Cc: stable@vger.kernel.org # 6.8
Fixes: b89b6a8 ("bus: mhi: host: Add spinlock to protect WP access when queueing TREs")
Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Jeff Hugo <jeff.hugo@oss.qualcomm.com>
Reviewed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Reviewed-by: Youssef Samir <quic_yabdulra@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Troy Hanson <quic_thanson@quicinc.com>
Link: https://lore.kernel.org/r/20250306172913.856982-1-jeff.hugo@oss.qualcomm.com
[mani: added stable tag]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Author: quic-jhugo

drivers/bus/mhi/host/main.c

@@ -1188,11 +1188,16 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 	struct mhi_ring_element *mhi_tre;
 	struct mhi_buf_info *buf_info;
 	int eot, eob, chain, bei;
-	int ret;
+	int ret = 0;
 
 	/* Protect accesses for reading and incrementing WP */
 	write_lock_bh(&mhi_chan->lock);
 
+	if (mhi_chan->ch_state != MHI_CH_STATE_ENABLED) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	buf_ring = &mhi_chan->buf_ring;
 	tre_ring = &mhi_chan->tre_ring;
 
@@ -1210,10 +1215,8 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 
 	if (!info->pre_mapped) {
 		ret = mhi_cntrl->map_single(mhi_cntrl, buf_info);
-		if (ret) {
-			write_unlock_bh(&mhi_chan->lock);
-			return ret;
-		}
+		if (ret)
+			goto out;
 	}
 
 	eob = !!(flags & MHI_EOB);
@@ -1231,9 +1234,10 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 	mhi_add_ring_element(mhi_cntrl, tre_ring);
 	mhi_add_ring_element(mhi_cntrl, buf_ring);
 
+out:
 	write_unlock_bh(&mhi_chan->lock);
 
-	return 0;
+	return ret;
 }
 
 int mhi_queue_buf(struct mhi_device *mhi_dev, enum dma_data_direction dir,